The sale fares also include longer routes, with the price of flights loosely tied to distance. Flights begin at $49 each way on Southwest’s shortest routes and increase to $79, $99 or $129 each way for longer flights.

The sale launched Tuesday morning, covering travel from Nov. 30 through Dec. 20 and from Jan. 4 through Feb. 15. Flights on Fridays and Sundays are excluded. The sale fares apply specifically to nonstop options, though many connecting itineraries may also show lower-than-usual fares.

Fares on some routes appeared to be even lower than the advertised $49 early Tuesday morning. Prices between Baltimore and Boston, for example, were showing on the carrier's website at just $41 each way -- or about $82 round-trip. Some Denver-Omaha round-trips were available for about $92.

Southwest’s new international routes are also included in the sale, though those routes come with significantly more restrictions. Fares range from $99 to $239 each way, depending on the route. But those prices are only offered on Tuesdays and Wednesdays. For those who can jump through those day-of-travel hoop, Southwest’s sale covers international flights from Nov. 30 through Dec. 13 and from Jan. 10 through March 2.

Either way, bargain seekers will have to act quickly to snag the fares. The sale ends on Thursday (Oct. 6) at 11:59 p.m. local time in city of the departing flight. (Full sale details)

The broad fare sale has become a staple for Southwest. It has rolled out similar 3-day sales each June and October for the past several years. One sale from June 2015 proved so popular that it crashed Southwest’s website, prompting the carrier to extend that particular sale by an additional 24 hours.

In a bit of extra good news for customers, Southwest’s latest sale that came out Tuesday rolled back restrictions the carrier had added to last broad sale in June. In that sale, Southwest offered its domestic sale fares only on Tuesdays, Wednesdays and Saturdays.

Southwest has used to sales to generate buzz and to sell seats during what are usually some of the slowest travel periods of the year.

In earlier versions of the sales, Southwest had pegged fares to mileage thresholds. Earlier this decade, for example, Southwest priced its sale fares at $49 each way for flights of 500 miles or less and prices increased from there. Flights of 501 to 1,000 miles cost $99 each way and flights of 1,001 to 1,500 miles cost $129 each way. Flights of more than 1,500 miles went for $149 each way.

Southwest ended the precise mileage component of its big sales a few years ago, but its big sales have continued to closely mimic its previous distance-based promotions. The carrier's four advertised sale-fare tiers for this sale — $49, $99, $129 and $149 each way — match the fares it offered on its distance-based sales of years past.